Biochemical Nitrogen Fixation Studies. III. Production and Oxidation of Ethyl Alcohol by Legume Nodules

Abstract

A series of experiments by both manometric and analytical methods has been conducted on the production and oxidation of ethyl alcohol by legume nodules and the data compared with similar data from small roots of legumes and of nonlegumes. The following results were obtained: 1. Ethyl alcohol was present in small amounts in all tissues studied. Under anaerobic conditions it accumulated and CO2 was evolved in approximately the proportions which would result from an alcoholic fermentation of sugar. 2. Under aerobic conditions, with alcohol added to the medium, part of the alcohol disappeared in a few hours and the R.Q. of the tissues was reduced by an amount depending on the concentration of the alcohol. At the higher concentrations it was commonly reduced nearly to that R.Q. (0.67) corresponding to the complete oxidation of alcohol. These results indicate that the alcohol which disappeared was oxidized completely. 3. Added alcohol increased oxygen consumption of both nodules and roots but not nearly enough to account for the change in R.Q. It is suggested that the alcohol consumption replaced and reduced the consumption of the other substrate present. 4. When glucose and alcohol were made available together in the medium, each affected the R.Q. in the same way as it did in the absence of the other, again without affecting the oxygen consumption proportionately, thus indicating that each inhibited competitively the oxidation of the other. 5. For nodules, either without added substrate or with glucose added, and for small roots with glucose added, the absence of a sparing action of oxygen on carbohydrate (and consequently of any oxidative reconversion of the products of fermentation to carbohydrate or similar compound) was indicated (a) by increased CO2 evolution and O2 consumption due to increasing concentrations of oxygen; (b) by similarly induced increases in carbohydrate consumption; (c) by a ratio equal to or greater than 3.00 between the CO2 produced under complete aerobiosis and that produced anaerobically; and (d) by the failure of the decreases, due to oxygen, in alcohol accumulation to exceed the carbohydrate oxidized. 6. On the contrary, for nodules with sufficient added alcohol and for small roots without added substrate or with alcohol added, the presence of a sparing action of oxygen on carbohydrate (in spite of increased total substrate consumption) was indicated by a decrease in carbohydrate consumption with increasing oxygen concentration and by a decrease in alcohol accumulation which was greater than the carbohydrate oxidized. Since the R.Q.'s indicate the absence of any oxidative reconversion of alcohol, it is suggested that the oxygen may have reduced in some way the primary breakdown of the carbohydrate. 7. The differences between the behavior of nodules and of roots in respiration are not thought to be fundamental. The roots behaved much like nodules with added alcohol. 8. The definite demonstration that alcohol is oxidized by the tissues of higher plants removes an important objection to considering it as an intermediate in normal plant respiration, but of course does not prove that it is an intermediate. 9. It is suggested that the occasionally observed sparing action of oxygen on carbohydrate in respiring plant tissues may be dependent on a high concentration of intermediate. If so, no fundamental difference in the mechanism of respiration need be assumed between that in tissues where the sparing action occurs and that in those from which it is absent.